The present invention relates to an ethylene polymerization process using a Ziegler-Natta type catalyst system.
According to EP-B-192 427 it is known to produce ethylene polymers by a gas phase polymerization process carried out in two consecutive polymerization reactors. According to this process, the catalyst used can be chosen from a wide variety of catalysts. However when this process is performed using a titanium based catalyst, ethane formation was very often observed in particular in the first reactor where hydrogen content is relatively high for producing polymers having a high melt index.
According to EP-A-197 689 it is known to polymerize olefins with a vanadium based catalyst used in the presence of chloroform as a catalyst promoter.
A process has now been found for the production of ethylene polymers carried out with a Ziegler-Natta type catalyst which makes it possible to substantially reduce the formation of ethane, in particular when a polymer having a high melt index is produced from a reaction mixture having a relatively high hydrogen content.